Circuit board and method of manufacturing same

Abstract

A circuit board having stable connection resistance can be obtained. The multi-layer circuit board includes the steps of making through-holes in a incompressible substrate having films on either side thereof via a bonding layer; filling conductive paste into the through-holes; removing the films from the substrate; laminating metallic foils to either side of the substrate and heating same under pressures to harden the bonding layer, bonding the metallic foils to the substrate and electrically connecting the sides of the substrate to each other; and forming a circuit pattern by machining the metallic foils.

1. A method of manufacturing a circuit board, comprising the steps of:
 (a) manufacturing an intermediate substrate, including the steps of:
 (i) manufacturing a substrate having incompressibility, 
 (ii) forming bonding layers on either side of said substrate, 
 (iii) forming a plurality of through-holes in said substrate, and 
 (iv) filling conductive paste into said through-holes; and 
 
 (b) manufacturing a double-side circuit board, including the steps of:
 (v) laminating metallic foils to either side of said intermediate substrate and heating same under pressures, and 
 (vi) forming a first circuit pattern and a second circuit pattern by processing said metallic foils. 
 
 
   
   
     2. The method of manufacturing a circuit board of  claim 1 ,
 wherein the step of manufacturing said substrate comprises a step of heating under pressures a composite material consisting of fiber aggregate and thermosetting resin impregnated to said fiber aggregate. 
 
   
   
     3. The method of manufacturing a circuit board of  claim 2 ,
 wherein said fiber aggregate contains at least one selected from the group consisting of inorganic fiber, ceramic fiber, organic fiber, and glass fiber. 
 
   
   
     4. The method of manufacturing a circuit board of claim  1 ,
 wherein the step of forming said bonding layer comprises the steps of: 
 laminating releasing films having a film material and adhesive disposed on said film material to either side of said substrate; and 
 removing only said film material from said substrate, 
 whereby said bonding layers are disposed on either side of said substrate. 
 
   
   
     5. The method of manufacturing a circuit board of  claim 1 ,
 wherein the step of manufacturing said intermediate substrate comprises the steps of: 
 disposing said bonding layer and film on either side of said substrate; 
 then, forming a plurality of through-holes in said substrate with said bonding layer and said film disposed thereon; 
 then, filling conductive paste into said through-holes, using the film as a mask; and 
 removing thereafter said film. 
 
   
   
     6. The method of manufacturing a circuit board of  claim 5 ,
 wherein said bonding layer remains on the surface of said substrate with said film material removed; and 
 said conductive paste equivalent in thickness to said film material is protruded from said bonding layer. 
 
   
   
     7. The method of manufacturing a circuit board of  claim 1 ,
 wherein said bonding layer in the above step (ii) is formed in a state of being half-cured. 
 
   
   
     8. The method of manufacturing a circuit board of  claim 1 , further comprising the steps of:
 (c) laminating a first intermediate substrate and a second intermediate substrate sandwiching therebetween a double-side circuit board manufactured in the above step (b), laminating a third metallic foil to the surface of said first intermediate substrate, and laminating a fourth metallic foil to the surface of said second intermediate substrate, 
 said first intermediate substrate and second intermediate substrate being same in configuration as said intermediate substrate manufactured in the above step (a); 
 (d) heating under pressures said third metallic foil, said first intermediate substrate, said double-side circuit board, said second intermediate substrate, and said fourth metallic foil which are laminated; and 
 (e) forming a third circuit pattern and a fourth circuit pattern by processing said third metallic foil and said fourth metallic foil, thereby manufacturing a four-layer circuit board. 
 
   
   
     9. The method of manufacturing a circuit board of  claim 8 ,
 wherein each of said first intermediate substrate and said second intermediate substrate has a protrusion of said conductive paste protruded from the surface of said bonding layer, and 
 in the above step (d), 
 the protrusion of said conductive paste is compressed, and said metallic foils disposed on either side of said intermediate substrates are electrically connected to each other by said conductive paste in said through-holes. 
 
   
   
     10. The method of manufacturing a circuit board of  claim 1 , further comprising the steps of:
 (f) laminating a first double-side circuit board and a second double-side circuit board sandwiching therebetween a first intermediate substrate, 
 said first double-side circuit board being said double-side circuit board, 
 said second double-side circuit board being same in configuration as said double-side circuit board, and 
 said intermediate substrate being same in configuration as said intermediate substrate manufactured in the above step (a); and 
 (g) heating under pressures said first double-side circuit board, said intermediate substrate, and said second double-side circuit board which are laminated. 
 
   
   
     11. The method of manufacturing a circuit board of  claim 1 , further comprising the steps of:
 (h) manufacturing a first bonding substrate and a second bonding substrate, 
 said first bonding substrate and said second bonding substrate having bonding layers disposed on either side of a first substrate, and 
 said first substrate having incompressibility; 
 (i) laminating said first bonding substrate and said second bonding substrate sandwiching there between said double-side circuit board manufactured in the above step (b), 
 laminating a third metallic foil to the surface of said first bonding substrate, and laminating a fourth metallic foil to the surface of said second boding substrate, 
 laminating a first bonding layer and a first releasing film to the surface of said third metallic foil, and 
 laminating a second bonding layer and a second releasing film to the surface of said fourth metallic foil; 
 (j) forming a plurality of non-through-holes in each of said first substrate, said first film, said second substrate, and said second film; 
 (k) filling conductive paste into said non-through-holes; 
 (l) removing said first film and said second film respectively from said bonding layers in a manner such that said first bonding layer and said second bonding layer respectively remain on said first substrate and said second substrate; 
 (m) disposing a third metallic foil on said first bonding layer, and disposing a fourth metallic foil on said second bonding layer; 
 (n) heating under pressures said third metallic foil, said first bonding substrate, said double-side circuit board, said second bonding layer, and said fourth metallic foil which are laminated; and 
 (o) forming a third circuit pattern and a fourth circuit pattern by processing said third metallic foil and said fourth metallic foil, thereby manufacturing a four-layer circuit board. 
 
   
   
     12. The method of manufacturing a circuit board of  claim 8 , further comprising the steps of:
 (h) manufacturing a first bonding substrate and a second bonding substrate, 
 said first bonding substrate and second bonding substrate having bonding layers disposed on either side of a first substrate, and said first substrate having incompressibility; 
 (p) laminating said first bonding substrate and said second bonding substrate sandwiching therebetween said four-layer circuit board manufactured in the above step (e), 
 laminating a third metallic foil to the surface of said first bonding substrate, and a fourth metallic foil to the surface of said second boding substrate, 
 laminating a first bonding layer and a first releasing film to the surface of said third metallic foil, and 
 laminating a second bonding layer and a second releasing film to the surface of said fourth metallic foil; 
 (q) forming a plurality of non-through-holes in each of said first substrate and said first film, and said second substrate and said second film; 
 (r) filling conductive paste into said non-through-holes; 
 (s) removing said first film and said second film respectively from said bonding layers in a manner such that said first bonding layer and said second bonding layer respectively remain on said first substrate and said second substrate; 
 (t) disposing a third metallic foil on said first bonding layer, and disposing a fourth metallic foil on said second bonding layer; 
 (u) heating under pressures said third metallic foil, said first bonding substrate, said four-layer circuit board, said second bonding layer, and said fourth metallic foil which are laminated; and 
 (v) forming a third circuit pattern and a fourth circuit pattern by processing said third metallic foil and said fourth metallic foil, thereby manufacturing a four-layer circuit board. 
 
   
   
     13. The method of manufacturing a circuit board of  claim 1 ,
 wherein the step of manufacturing said intermediate substrate comprises a step of filling said conductive paste into said through-holes in a manner such that said conductive paste includes a protrusion from the surface of said bonding layer, and 
 in the above step (v), the protrusion of said conductive paste is compressed by said metallic foil, and 
 said metallic foils disposed on either side of said intermediate substrates are electrically connected to each other by said conductive paste in said through-holes. 
 
   
   
     14. The method of manufacturing a circuit board of  claim 1 ,
 wherein said bonding layer is in a range of about 5 μm to about 15 μm in thickness. 
 
   
   
     15. The method of manufacturing a circuit board of  claim 1 ,
 wherein the bonding layers disposed on either side of said substrate are different in thickness. 
 
   
   
     16. The method of manufacturing a circuit board of  claim 1 ,
 wherein the step of forming a substrate having incompressibility further comprises a step of roughening the surface of said substrate before forming said bonding layer. 
 
   
   
     17. The method of manufacturing a circuit board of  claim 1 ,
 wherein the step of forming a substrate having incompressibility further comprises a step of eliminating residual stresses. 
 
   
   
     18. The method of manufacturing a circuit board of  claim 1 ,
 wherein the step of forming a substrate having incompressibility further comprises a step of heat-treating said substrate at the glass transition temperature of resin contained in said substrate, whereby residual stresses of said substrate are eliminated. 
 
   
   
     19. The method of manufacturing a circuit board of  claim 1 , further comprising the step of:
 (w) disposing a smoothing layer on the bonding layer in concavities of at least one circuit pattern of said first circuit pattern and said second circuit pattern of said double-side circuit board. 
 
   
   
     20. The method of manufacturing a circuit board of  claim 19 ,
 wherein said smoothing layer contains resin. 
 
   
   
     21. The method of manufacturing a circuit board of  claim 8 , further comprising the step of:
 (x) forming a smoothing layer on the bonding layer in concavities of at least one circuit pattern of said first circuit pattern and said second circuit pattern of at least one double-side circuit board of said first double-side circuit board and said second double-side circuit board, 
 wherein the smoothing layer side is placed on said first intermediate substrate. 
 
   
   
     22. The method of manufacturing a circuit board of  claim 21 ,
 wherein the process of forming said smoothing layer comprises the steps of: 
 forming half-cured resin in the concavities, and 
 laminating said double-side circuit board having said smoothing layer containing the half-cured resin to said first intermediate substrate.